Patients with SLE make pathogenic subsets of autoantibodies, including anti-DNA (aDNA), which can induce nephritis. We hypothesize that upregulation of those subsets occurs partly because helper T cells recognize determinants on the surface immunoglobulin (Ig) of B cells, probably after the B cell processes the Ig into peptides which are presented in surface MHC Class II molecules. Since some pathogenic aDNA can be identified in this B cell-T cell cross-activation. This proposal combines the expertise of two laboratories which have identified public Ids that are enriched in autoantibodies associated with both murine and human lupus nephritis. Specifically, we will 1. prepare monoclonal (Mab) aDNA from SLE patients by EBV immortalization of their B cells, 2. sequence the variable (V) regions of their Ig heavy (H) and light (L) chains, 3. characterize selected Mabs as pathogens or nonpathogens by measuring their ability to induce clinical nephritis in BALB/c mice, 4. synthesize peptides that contain amino acid (AA) sequences common to Id+ Mabs, to pathogens, or to anti-dsDNA, then test those peptides for their ability to activate autologous T cells, 5. clone responding T cells and analyze their phenotypes and ability to help B cells secrete pathogenic Ig, and 6. determine the frequency of expression of Ig containing these stimulatory peptides in B cells from patients with SLE, correlating results with clinical characteristics. Identification of regulatory idiopeptides should provide new information regarding the pathogenesis of SLE, and should suggest new strategies to specifically interfere with recognition of those peptides. Therefore, this proposal fits the theme of the program project. These experiments require the services of both the peptide synthesizing and the cell sorting/FACS cores.